1. Field of the Invention
The invention relates to a method for producing fibrous materials from thermoplastic materials, wherein the thermoplastic material is melted and fed into a rotating reactor for the formation of a molten film and the fibers are formed on and stretched out along an open edge of the reactor.
The invention also relates to a device for producing fibrous materials from thermoplastic materials with a melting apparatus for the thermoplastic material and a heated rotating reactor for forming of a molten film from the melted plastic, which exits the rotating reactor over an edge of an open side as fibers are formed.
2. Detailed Description of the Prior Art
Non-wovens made of fibrous materials of this type are used in particular for the absorption of petroleum, petroleum products and heavy metal ions from water. For especially effective nonwovens it is desirable for the fibers to have as small a thickness as possible.
The standard type of production of thermoplastic fibers is accomplished by melting down the starting thermoplasts and extruding the molten plastic through thin nozzles to form thin straight fibers. By stretching them out, the extruded fibers can be made even thinner, while they are simultaneously cooled down using a special airstream. These methods assume a very homogeneous starting thermoplast so that the use of recycling plastics, which are dishomogeneous and can contain foreign matter, is excluded from consideration. In particular, they would clog the nozzles. The extrusion processes also provide for working at relatively low temperatures, which can be only slightly higher than the melting temperature, in order to configure the cool-down measures following extrusion as simply as possible. By contrast, processing secondary raw materials and thermoplastic wastes requires high temperatures, which are close to thermoplastic decomposition temperatures.
Known in particular from SU 699 041 is the feeding of the themoplast melts to a revolving pot on the inner wall of which the molten film forms, and the stretch-spinning from the melted film is accomplished by the formation of fibers on the edge of the drum using a gas conducted over the molten film at high speed. The reactor here is designed in the form of a vertically positioned pot and consists of a hollow space and a work surface. Heated gas is fed under pressure to the interior hollow space of the reactor and the surface of the molten film. On the edge of the drum are slotted nozzles through which the molten film is divided up into individual streams and flows together with the heated gas. In this way the formed streams are made thinner and stretched out.
The object of the invention is to be able to create thin synthetic fibers that can be formed in high yields from high quality raw materials, but can also be formed from waste thermoplasts, all while avoiding the disadvantages of the known device.
To reach this goal, a method according to the invention of the type mentioned in the introduction is characterized in that the rotating reactor is heated so that the molten film has a temperature near the decomposition temperature of the thermoplastic material and in that the reactor is rotated at a belt speed of at least 10 m/s at its edge.
According to the invention, the reactor is thus heated itself so that the molten thermoplast is subjected to very constant temperature conditions, which can be selected close to the decomposition temperature for the thermoplasts without there being a risk of affecting the quality of the plastic stemming from particular localized areas exceeding this temperature, thereby leading to instances of decomposition. The fiber formation in the method according to the invention is a result of the high rotational speed or the high belt speed at the edge of the reactor, which causes the cohesive force of the molten film to be exceeded so that the division into fibers is accomplished. The use of channels or nozzles that are prone to clogging can therefore be completely done away with.
The fibers stretched out on the edge of the rotating drum are appropriately stabilized by the effect of an airstream that preferably runs transverse to the course of the fibers.
The thermal uniformity in the reactor required for the method according to the invention is supported in a preferred embodiment by the inner space of the reactor being closed off to a large extent by a cover forming a narrow circumferential gap with the edge. The gases that flow out when the molten film is heated up exit through the gap and positively influence the formation of fibers according to the invention. The cover is preferably fixedly positioned for this. It can be useful in this case for the cover to be positioned asymmetrically with respect to thereactor""s axis of rotation to form a circumferential gap with a varying width.
With a smooth inner reactor surface the molten film could form spiral schlieren, thus irregular thicknesses. This can largely be prevented by subdividing the molten film on the inner reactor wall by means of axially oriented ribs.
To resolve the aforementioned problem, a device of the type mentioned in the introduction is also characterized in that the rotating reactor is heated from the outside and is sealed on its open side by an affixed cover up to a circumferential annular gap formed with the edge.
To strengthen the acceleration of the molten film, it is advantageous for the inner wall of the rotating reactor to expand conically toward the edge, whereby the reactor can neverthelessbe cylindrically shaped over the largest portion of its axial length.
The annular gap can preferably have a width of 15 to 20 mm, whereby the gap can be formed with a varying width by arranging the cover asymmetrically with respect to the rotating reactor""s axis of rotation.
When the inner wall of the reactor is provided with axially oriented ribs to subdivide the molten film, according to a preferred embodiment of the invention, these are preferably configured with a triangular shape having its greatest height at the base of the reactor and having its lowest height at the end where the molten film exits. In connection with the preferred embodiment of a cylindrical reactor, which expands conically toward the open end, the ribs preferably extend over the cylindrical part of the reactor and terminate at the beginning of the conical part.
The reactor is heated up to its operating temperature from outside by means of a heater, which preferably can be a resistance heater, an induction heater or a magnetic induction heater.